Volume control for amplifiers



June 30, 1936. 5 BALLANTmE 2,046,237

VOLUME CONTROL FOR AMPLIFIERS Filed July 5, 1929 4 Sheets-Sheet l 3dGrid Wm H afkoznetgo.

J1me 1936- s. BALLANTINE 2,046,237

VOLUME CONTROLFOR AMPLIFIERS Filed July 5, 1929 4 Sheets-Sheet 2 Rad/'0Frequency 07,011) l/faqe gwowntot:

June 30,)936. I s BALLANTINE 2,046,237

VOLUME CONTROL FOR AMPLIFIERS Filed July 5, 1929 4 Sheets-Sheet 5 June;30, 1936, s. BALLANTINE VOLUME CONTROL FOR AMPLIFIERS Filed July 5, 19294 Sheets- Sheet 4 f a g mama: AMA 3 v f g 7 z i I Patented June 30, 1936UNITED STATES VOLUME CONTROL FOE AMBLIFIEBS Stuart Ballantine, ,MountainLakes, N. 1., assignor, by mesne assignments, to Radio Corporation ofAmerica, Duration of Delaware New York, N. Y., a cor-- Application July5, 1929, Serial No. 376,163

41 Claims.

This invention relates to methods oi,-and apparatus for, controlling thetransmission in amplifiers, and particularly to methods of, andapparatus for, extending the range of amplification control inmulti-stage amplifiers throughout which distortionless amplification maybe obtained.

It has been customary to control the amplification oi'an amplifier stageby varying theener gizing voltage impressed upon an electrode of theamplifier tube, for example the grid bias, and in the case of cascadedradio frequency, or carrier wave; amplifiers, a wide range of controlhasbeen secured by simultaneously varying the bias on the grids of all ofthe amplifier tubes. This conventional method of controlling radiofrequency amplification is described in my copending application Ser.No. 231,273, filed Nov. 5, 1927 patented July 26, 1932 as U.,S. PatentNo. 1,869,331, relating to a method of, and apparatus for, automaticallycontrolling the amplification in accordance with received signal energy.It has been found experimentally, however, that if the several grids arebiased equally, a value of common grid bias is reached at which therelation between the input and output voltages of the amplifier becomesnon-linear.

Objects of the present invention are to provide methods of, andapparatus for, maintaining distortionless amplification while varyingthe amplification over a wide range. Further objects are to increase therange of amplification control throughout which cascaded stages operateas a linear amplifier. More specifically, objects of the invention areto provide a method of, and apparatus for, amplification control whichwill increase the upper limit which the input signal voltage may reachbefore the distortion becomes objectionable.

These and other objects of the invention will be apparent from thefollowing description, when taken with the accompanying drawings inwhich:

Figs. 1 and 2 are diagrams comprising curves representing the relationbetween input voltage and output voltage.

Fig. 3 is a diagram illustrating the ranges through which the biasvoltages of successive stages may be varied while maintainingdistortionless amplification,

Figs. 4, 5, and 6 are fragmentary diagrams of cascaded amplifiercircuits embodying the invention.

The novel features which I'believe to be characteristic of my inventionare set'forth in particularity in the appended claims, the inventionitself, however, as to both its organization and method of operationwill best be understood by reference to the following description takenin connection with the drawings in which I have indicateddiagrammatically several circuit organizations whereby my invention maybe carried into effect.

The curves of Fig. 1 were plotted from data taken with a four-stageradio-frequency amplifier which had been designed to supply a maxi- 10mum of 20 volts to a high-voltage linear detector. The amplitude was tohave been maintained at 10 volts, the 20 volt limit being set to takecare of 100% modulation, The various curves represent the relationbetween the radio 15:

frequency output and input voltages for various grid bias voltages, theparticular bias voltage which was common to all stages being indicatedon Fig. 1 adjacent the respective curves.

It will be seen that the amplifier system re- 20 mains linear until thebias voltage reaches about 9 volts, and that it departs rapidly fromlinearity as the common negative bias is extended beyond that point.Considerable distortion occurs when the control voltage is made highly25 negative to reduce the amplification for strong input signals, andeven if the output voltage were maintained at 10 volts by automatic ormanual control of the common grid bias, the audio output of the detectorwould not be constant since 30 the cut-off efiect shown in Fig. 1effectively increases the degree of modulation of the signals.

These effects become of importance when the input signal level is high(as, for example, when the radio receiver is located near a transmittingstation), and their effect is to limit the range of control; that is, tolimit the range of input voltage over which the signal may vary beforedistortion appears.

Thebasis for the method of control which I employ may be understood froma consideration of the curves of Fig. 2, which set of experimentalcurves shows the relation between radio frequency input and outputvoltage for a single stage 01- an amplifier. It is to be noted that thecurves are plotted with logarithmic coordinates in order that a widerange of voltages may be represented. Each curve represents the relationbetween radio frequency input and output voltages for a fixed grid bias,the value 01' the bias for each curve being indicated adjacent thatcurve on Fig. 2.

It will be seen that up to a certain point, for any given bias voltage,the relation between radio frequency input and output voltage isapproxi- 7 gion of distortionless operation. To avoid distortion in acascaded amplifier, the grid bias and the radio frequency input voltageof each stage must be so related that they lie to the left of thebounding curve RE, that is, in the region of linear response. Thestraight line RT completes the boundary and represents the residualtransmission through the amplifier stage, which is, of

course, linear, and which may arise in several ways.

In a shielded tetrode stage without provision for neutralizing theeffect of a small residual unshielded plate-to-control-grid capacity, itwould arise from the electrostatic coupling through this capacity. Inthe case of an ordinary unshielded triode with a balancing network, itmay arise from a slight unbalance, intentional or accidental. It mayalso be intentionally provided by coupling in the circuits external tothe tube. This leakage is often useful in adjusting the linear boundary,and it permits the use of higher radio frequency input voltages withoutdistortion.

The set of curves of Fig. 2 reveals the important fact that the higherthe radio frequency voltage output desired from the stage, the smallerbecomes the range over which the amplification can be varied. Since thevoltages in all stages are different, operation in accordance with thepresent invention comprises controlling the overall amplification overthe broadest permissible range by a graduated variation'of theampllfication in the individual stages, the ranges of control for theindividual stages being so chosen as to keep all stages in the region oflinear response. The burden of control is thus placed upon the stages inwhich the signal voltages are lowest, and in this way the range ofcontrol is extended far beyond that which is possible in the knownarrangements in which the biases ofall stages are equal, or are variedat the same rate.

This considerable extension of the range of distortionless control isshown graphically in Fig. 3, which is a diagram showing the voltages tobe applied to the various grids of an amplifier comprising cascadedstages of the characteristics shown in Fig. 2.

It is assumed that a high voltage detector is connected to the outputterminals of the final radio frequency stage and that the maximum outputto the detector is to be 20 volts. On the Fig. 3 diagram, the fixedpoint D indicates this value of 20 volts at which the amplifier outputbias were varied at the same rate on alltubes,

the limits of the range of variation, without distortion, at the inputterminals of the amplifier, will be represented by points A and G, sincethe small variation which is permitted in the final stage limits theranges of control on the first and second grids to the regions A'G andBF, respectively.

By departing from the prior practice of emaosaasv ploying a common gridbias for all stages, the range of control is extended for the first andsecond stages. Distortion in the final stage is elimi-' nated byrestricting the output voltage of the preceding stage to a maximum of2.2 volts, point C 5 in Fig. 3. The data of Fig. 2 shows that the biasof stage 2 may be increased negatively until the input voltage for thatstage attains a value of 1 volt, point B, Figs. 2 and 3. Similarly, inFig. 2 the curves show that for an output of 1 volt, the 10 inputvoltage for the first stage may be 0.75 volt, point A. The range ofcontrol has thus been extended to the value AG, Fig. 3, and it will beseen that its magnitude is enormously greater than the range A'G whichis permissible when common bias voltages are employed.

In the circuit diagram which illustrates the invention as embodied in aradio receiver of the type including an automatic volume control, Fig.4, only those parts which are of interest in connection with the presentinvention are shown in heavy lines.

The receiver includes three tuned radiofrequency amplifier stagesemploying tetrodes, or screen grid tubes, T1, a triode detector, and two25 audio amplifier stages. These tubes, and the rectifier tube T: whichforms part of the auto- III ' matic volume control system, are of thealternating current type, and the circuits (not shown) for supplyingcurrent to the tube heaters may be of the usual type.

So far as radio frequency currents are con-' cerned, the low potentialsides of all circuits are at ground potential, being terminated at theshielding, or ground, line I. Plate current is supplied from batteries,or preferably a power supply device, not shown, which is connectedacross terminals +B, B. An intermediate point of the voltage divider 2,which is shunted across the plate supply terminals, is connected to theground line I by a lead 3.

The automatic volume control is applied only to the first two radiofrequency stages, the inductance L: of. the third stage being connecteddirectly to the ground line I, while the inductances La of the precedingstages are grounded through by-pass condensers C. The cathode circuitsof the radio frequency stages include grid bias resistors 4 whichdetermine the bias on the third stage and the normal operating point forthe first two stages.

The operating potentials for the volume control tube T2 are obtained byconnecting the oathode, through lead 5; to a point in voltage divider 2at which the direct current potential is less than that of the groundinglead I; the anode of tube T: being connected through series resistancesB,

I and lead Ste-the ground line I, and the grid being connectedthroughleak resistance 9 and so adjustable contact III to that portion ofvoltage divider which is at less than ground potential.

The grid of the volume control tube '1: is connected, through condenserI I and lead I 2, to the grid of the detector tube, and the output ofthe tube T2 is applied to the low potential'tenninals of the inductancesL: of the first two stages by leads ll, II respectively.

In accordance with the present invention, the range of control impressedupon the stage is graduated by connecting lead I 3 to the anode of thecontrol tube, and lead I I to the Junction of series resistances 8, 1.

As explained in my aforesaid patent, the output 15 the bias voltage ofthe second tube may be varied is less than the bias voltage range of thefirst tube.

The value of carrier voltage at which the automatic control starts tofunction is regulated by the variable bias voltage tap ill of tube T2.The input voltage regulator I5 is provided to keep strong signals fromexceeding the upper limit of distortionless control, point A, Fig. 3.

The invention is equally applicable to multistage amplifiers in whichthe amplification control is effected by the variation of the othervoltages of the tubes, either in conjunction with a simultaneousvariation of the grid bias, or separately.

For example, Fig. 5 illustrates the application of the invention to acascaded amplifier in which the control of amplification is effected byvarying the potentials impressed upon the screen-grids of tetrodes. Thegeneral circuit arrangement of the amplifier forms no part of theinvention, and, therefore, will not be described in detail.

The volume control circuit elements are shown by heavier lines, andcomprise a battery IE, or other suitable source of current, and a seriesof voltage dividers for regulating the voltages impressed upon thescreen-grids G2 of the cascaded tetrodes T1, T2, T3. The resistanceelements H of the voltage dividers are of identical construction, andthe switch arms I8 are mounted on a common shaft for simultaneousoperation by a suitable volume control knob, or dial, l9. In accordancewith the present invention, the several switch arms iii are insulatedfrom each other by non-conducting sections 20 of the operating shaft,and the switch arms are angularly displaced from each other to place,for all adjustments of the control device, progressively higher voltagesupon the screen-grids of the succeeding tetrodes of the cascadedamplifier. The angular displacement of the contact arms I8 is so chosen,with respect I trodes of cascaded tubes.

to the changing slope of the'gain-control voltage characteristic of thetetrodes, that the operating pointsof succeeding stages fall uponportions of the curve which are of different slope.

For a given angular adjustment of the control knob l9, the controlvoltages are all changed by equal increments, but the changes inamplification are not equal in the several stages, being progressivelysmaller in succeeding stages.

As shown in Fig. 6, the control device-for an amplifier circuit, of thegeneral type illustrated in Fig. 5, may comprise a gang voltage dividerhaving a series of identical resistances I1 and aligned contact arms l8when progressively higher voltages from the current supply source iiiare impressed across the resistances ll of succeeding stages. Althoughthis arrangement produces progressively greater changes of controlvoltages in succeeding stages, the corresponding changes inamplification are progressively smaller since the several tetrodes areoperating upon different portions of their characteristic curves.

The specific control circuits which I have described illustrates thegeneral applicability of the basic invention to the various typesofamplification control which are based upon a regulation of the operatingpotentials impressed upon the elec- It will be apparent to thosefamiliar with the design and construction of amplifiers that thegraduated amplification control may be provided in cascaded amplifiersin which the overall amplification is regulated by varying the platepotentials, or the cathode, or cathode heater, potentials in a pluralityof stages.

The invention contemplates the graduation of the ranges of control in acascaded amplifier, and it will be apparent that there is wide latitudein the choice of the electrical circuits and the me-,-

chanical details of the apparatus which may be employed for varying, atdifierent rates, the amplification of the individual stages of acascaded amplifier. It is therefore to be understood that controlcircuits and control apparatus other than the specific embodimentsdescribed herein fall within the scope of my invention as set forth inthe following claims.

I claim:

1. In a. transmission system including cascaded tube stages foramplifying an incoming signal at radio frequency, the method ofmaintaining a uniform and distortionless transmission level whichcomprises simultaneously varying the amplification of theseveral stagesat different rates. 2. In the operation of a tube amplifier including aplurality of stages for successively amplifying an incoming wave withoutchange of frequency, the method of extending the range throughout whichdistortionless volume control may be efiected which comprisesprogressively decreasing the range of control in successive stages ofsaid amplifier.

3. In the operation of cascaded amplifier stages for amplifying anincoming wave at radio frequency and of the type having linear andnonlinear response ranges, the method of maintaining an overall linearamplification while controlling the output volume, which comprisesgraduating the volume control impressed upon the separate stages inaccordance with the range of linear response of the respective stages.

4. In the process of .varying the amplification of cascaded radiofrequency amplifier stages by impressing upon an element of each stagea; control voltage derived from and varying in magnitude with receivedsignal energy, the method which comprises progressively decreasing therange of control voltages impressed upon succeeding stages.

5. In a transmission system including cascaded amplifier stagesoperating at the same frequency, the method of maintainingdistortionless amplification while varying the overall amplifica tionwhich comprises-determining for a; predetermined maximum output thelimits of the respective ranges of linear response of the individualstages, and adjusting the range of values of the variable volume controlelements of the individual stages to maintain the operation of eachstage within its respective range of linear response.

6. The combination with a plurality of cascaded tube amplifier stagesoperating at the same frequency, of volume control means automaticallyresponsive to signal amplitude variations for effecting progressivelysmaller changes in the amplification of succeeding stages. v

'7. An electrical transmission system of thetype including a pluralityof cascaded tube amplifier stages all amplifying received energy at thesame frequency, and means automatically responsive to signal amplitudevariations for varying an energizing voltage of each stage to controloverall 7 5 amplification of .said system, characterised by the factthat said amplification means includes elements progressively decreasingthe range throughout which the energizing voltages of succeeding stagesmay be varied.

'8. The combination with a plurality of cascaded amplifier stages forsuccessively amplifying incoming energy at its received frequency. ofmeans automatically responsive to signal amplitude variations forvarying an amplification-controlling voltage applied to each of saidstages, and

circuit elements in said voltage-variation means for progressivelydecreasing the voltage changes applied to successive stages.

9. The invention as set forth in claim 8, wherein said voltage-variationmeans comprises a tube rectifier, an input circuit for said rectifierand shunted across the output of said amplifier.

stages, and connections for applying the output of said rectifier to thegrids of said stages; and said circuit elements comprise resistance inthe rectifier output circuit.

10. The combination with a cascaded tube amplifier, and means forrectifiying carrier wave energy to produce a direct current output, ofcircuit connections for impressing upon a tube element in each of a.plurality of stages a potential determined in magnitude by the directcurrent output, and means for progressively decreasing the magnitude ofthe voltage so impressed upon succeeding stages.

.11. The invention as set forth in claim 10 wherein said rectifier meanscomprises a tube having a resistance in the plate circuit thereof, andthe circuit connections are so made to spaced points in said resistancethat a lesser fraction of the voltage, drop across said resistance isapplied to succeeding stages of said amplifier.

12. In an electrical transmission system-of the carrier wave type, aplurality of cascaded-tube amplifier stages, a ground line and circuitconnections for maintaining the low potential terminals of the inputcircuits of said stages at the carrier wave potential of said groundline, resistors in the cathode circuits of said stages for establishim anormal direct current bias of said stages, and means automaticallyresponsive to signal amplitude variations for varying the bias voltagesof said stages, said means varying the bias voltage of succeeding stagesover progressively smaller ranges.

' each successive stage, and a common control Iiiv means automaticallyresponsive to Signal amphtude variations for varying all of said meanssimultaneously. I

15. Areceiver for high frequency signal waves including a detector, atleast two tube amplifier stages preceding said detector, anelectrondischarge tube rectifier circuit with a signal connection to thedetector input, said rectifier circuit including means for developing adirect current potential from signals impressed on the rectifier, andconnections from the rectifier circuit means to an input electrode ofeach stage for iml device is varied at a difi'erent rate.

pressing thereon direct cm'rent control potentials of suchdifierentmagnitudes as to maintain substantially constant the signalenergy supplied to said detector input. Y

16. A receiver for high frequency signal waves 5 including a detector,at least two tube amplifier stages preceding said detector, an electrondischarge tube rectifier circuit with a signal connection froma coldelectrode thereof to the detector input, means for maintaining thecathode of the rectifier tube positive with respect to said coldelectrode, said rectifier circuit including means for developing adirect current potential from signals impressed on the rectifier, andconnections from the rectifier circuit means to an input electrode ofeach stage for impressing thereon direct current control potentials ofsuch different magnitudes as to maintain substantially constant thesignal energy supplied to said detector input.

1'1. 'A receiver for high frequency nal waves including a detector, atleast two tube amplifier stages preceding said detector, an electrondischarge tube rectifier circuit with a signal connection to thedetector input, said rectifier circuit 25 including means for developinga direct current potential from signals impressed on the rectifier, andconnections from the rectifier circuit means to an input electrode ofeach stage forimpressing thereon direct current control potentials ofsuch 30 different magnitudes as to maintain substantially constant thesignal energy supplied to said detector input and manually controllablemeans connected to at least'one of the amplifier stages for regulatingthe maximum signal strength transmitted to said detector.

18. In a system for converting alternating current into uni-directionalcurrent of the type comprising a plurality of preceding space dischargedevices followed by a rectifier and a.final load v4o circuit, a net workfor automatically controlling the transmission efficiencies of saiddevices comprising a rectifier provided with an alternating currentinput circuit coupled to the input of said first rectifier, and directcurrent output circuits 45 connected to ton control elements of saiddevices from different direct current potential points of said secondrectifier circuit in such a manner that the on efiiciency of each 19. Ina system for converting alternating current into uni-directional currentof the type comprising a plurality of preceding space discharge devicesfollowed by a rectifier and a final load circuit, a network forautomatically controlling the transmission eillciencies of said devicescomprising a rectifier provided with an alternating current inputcircuit coupled to the input of said first-rectifier and. direct currentoutput circuits connected to on control elements of on said devices fromdifferent direct current potential points of said second rectifiercircuit in such a manner that the on efilciency of each device is variedat a different rate and means for predetermining the value ofalternating current intensity at which said network starts to function.20. In a high frequency amplifier system, a plurality of screen gridtubes arranged in cascade, means for supplying at least one of the coldelectrodes of each of said tubes with negative energizing potentialsprogressively decreasing for each successive stage, and a common controlmeans automatically responsive to signal amplitude variations forvarying all of said means simultaneously. 1s

21. In a high frequency amplifier system, a plurality of screen gridtubes arranged in cascade, means for supplying a signal control gridelectrode of each of said tubes with negative energizing potentialsprogressively decreasing for each successive stage, and a common controlmeans automatically responsive to signal amplitude variations forvarying all of said means simultaneously.

22. In a high frequency amplifier system, a plurality of screen gridtubes arranged in cascade, means for supplying the screen grid electradeof each of said tubes with positive energizing potentials progressivelyincreasing for each successive stage, and a common control means forvarying all of said means simultaneously.

23. In a high frequency amplifier system, a

plurality of screen grid tubes arranged in cascade,

means for supplying at least one of the cold electrodes of each of saidtubes with positive energizing potentials progressively increasing foreach successive stage, and a common control means for varying all ofsaid means simultaneously.

24. In an amplifier system, a plurality of electric discharge devicesvhaving grid elements, means for automatically causing biasingpotentials to be impressed on said grid elements at unequal rates withrespect to each other in response to changes in carrier intensity, thegreater rate of change occurring on the grid of the device normallyexperiencing the least signal potentials.

25. In an amplifying system having a plurality of amplifying stages intandem, a control circuit comprising an electric discharge device havingan input and an output circuit, a resistor in said output circuitassociated in varying degrees with the grid circuits of said amplifyingstages, the earlier stages being associated in greater degree with saidresistor than subsequent stages, whereby a change'in the input circuitof said electron discharge device will produce unequal changes in theamplifier characteristics of said amplifying stages, respectively inproportion to the degree of association.

26. In the operation of an electrical wave amplifier working into arectifier and subject to signals of varying magnitude, the method ofautomatically controlling the gain of said amplifier,

which comprises impressing upon the amplifier input circuit two discretedirect current potentials which vary automatically and according todifferent functions of the magnitude of the incoming electrical wave,one of said potentials being predominately effective for weak signalsand the other predominately effective for strong signals.

27. In automatic volume control apparatus wherein two discretepotentials are employed to control amplifier gain, means whereby one ofsaid discrete potentials is obtained by rectification of the amplifieroutput, and means whereby the second potential is derived from thespaces current flow in the cathode circuit of the amplifier.

28. The method of operation of an electrical wave amplifier so as tosecure automatic gain control thereof, which comprises applying to saidamplifier a gain control potential which varies automatically with themagnitude of the input of said amplifier and applying to said amplifiera second gain control potential which varies automatically as a functionof said first gain control potential.

29. The method of operation of an electrical wave amplifier so as tosecure automatic gain to succcessive stages, said voltage variationmeans said aforementioned circuit elements comprising resistance in therectifier output circuit, and a I automatically with the magnitudfofthelr'i'put of said amplifier and applying to said amplifier a. secondgain control potential which varies auto- 5 matically as a function ofsaid first gain control potential, said second gain control potentialbeing obtained by the voltage drop due to the fiow of current in thecathode circuit of said amplifier. 30. The method of 'operation of acarrier wave amplifier receiving electrical signals of varyingmagnitudes was to secure an automatic control of the gain of saidamplifier, which comprises impressing a direct current potentialgvaryingwith signal strength upon the input circuit thereof and 15 impressingupon said input circuit a second direct current potential automaticallydecreasing in magnitude as the strength of the received electric-signals increases, both of said direct current potentials functioningvas gain control voltages. 20

31. "The combination'with a plurality of cascaded amplifier stages whoseinput circuits are maintained at a common carrier wave frequency,

'of means for varying an amplification-controlling voltage applied toeach of said stages, circuit elements in said voltage-variation meansfor pro'- gressively decreasing the voltage change applied to successivestages, said voltage variation means comprising a tube rectifier, aninput circuit for said rectifier shunted across the output of saidamplifier stages, connections for supplying the output of said rectifierto the grids of said stages, said aforementioned circuit elementscomprising resistance in the rectifier output circuit, and a detector"tube havingits input circuit connected to said amplifier output and therectifier' input circuit. I

32. The combination with a plurality of cascaded amplifier stages whoseinput circuits are maintained at a common carrier wave frequency, ofmeans for varying an amplification-controlling voltage applied to eachof said stages, circuit elements in said voltage-variation means for progressively decreasing the voltage change applied comprising a tuberectifier, an input circuit for. said rectifier shunted across theoutput of said amplifier stages, connections for supplying the output ofsaid rectifier to the grids of said stages,

detectortube having its input'circuit' connected to said amplifieroutput and the rectifier input circuit, and means for varying thetransmission efiiciency of said rectifier tube.

33. In a high frequency signal transmission system, a plurality ofelectron discharge tube stages arranged in cascade, means for supplyingat least one of the electrodes of each of at least two successive tubeswith a positive energizing potential, the potential applied to thesecond of the successive tubes being the greater in magnitude, means forsimultaneously varying the magnitudes of said potentials, the constantsof said successive tubes being chosen to cause the changes inamplification thereof to be progressively smaller.

34. In a high frequency signal transmission system, a plurality ofelectron discharge tube stages arranged in cascade, means for supplyingat least one of the electrodes of each of at least two successive tubeswith a positive energizing potential, the potential applied to thesecond of the successive tubes being the greater in magnitude, means forsimultaneously varying the magnitudes of said potentials by equalincrements, the constants of said successive tubesbeingchosentocause-thechangesinamplificationthereoftobep srflivelynnaller.

35. In ,a high frequency si nal tra system, a plurality of electrondischarge tube stages arranged in cascade, means for supplying at leastone of the electrodes of each of at least two successive tubes with apositive energizing potential. the potential applied to the second ofthe successive tubes being the greater in magnitude, means forsimultaneously varying the magnitudes of said potentials byprogressively increasing increments, the constants of said successivetubes being chosen to cause the changes in amplification thereof to beprogressively smaller.

36. In an electrical wave on system employing electron discharge tubesin cascade, the method of controlling the wave tran through said tubeswhich includes deriving a direct current voltage from the waves whichvaries in magnitude with the amplitude of the latter, and varying theamplification of the tubes with said voltage so that the amplificationof the first tube varies to a greater extent than that of any of thetubes following.

37; In a radio receiver employing electron discharge tubes in cascade,the method which comprises automatically varying the amplification of atleast two of the tubes in response to received signal carrier amplitudevariations. and simul-. taneously causing the change in amplification ofthe first of the two tubes to occur at a greater rate.

38. In a radio receiver of the type including means amplifying receivedsignals at radio frequency, a network for deriving from the amplifledsignals avvoltage representative of the. signal modulation in stillfurther amplified form, means for further amplifying the amplifiedmodulation representative voltage, means responsive to signal carrieramplitude variations for automatically ad- Justing the amplification orthe first means, and an auxiliary manually variable device, connectedbetween said network and the modulation voltageampliiying means, forcontrolling the trans- 1nili'iistziron or amplified modulation voltageto the 89. In a radio receiver having a demodulator, sapluralityoi'tubesarrangedincascadetotransmit received signals inamplified form to the demodulator input, an audio amplifier, anautomatic volume control network constructed and arranged to, vary thegain oi. the first of the cas- 1o cadedtubestoagreaterextentthanthatofthe following tubes, adjustable means other thansaid network for varying the intensity of the signals transmitted to thedemodulator, and means between the demodulator output and said audioamplifier for adjusting the intensity of the audio signals transmittedto the audio amplifier. 7 40. In a radio receiver of the ype ncludingmeans amplifying received modulated signals at radio frequency, anetwork for deriving-from the amplified signals a voltage representativeof the signal modulation, means for amplifying the mod-' 'ulationrepresentative voltage, means responsive to signal carrier amplitudevariations for automatically adjusting the amplification of the firstmeans, and an auxiliary manually variable device, connected between saidnetwork and the modulation voltage amplifying means, for con trollingthe n of modulation voltage to the latter.

41. In a radio receiver having a demodulator, a plurality of tubesarranged in cascade to transmit received signals in amplified form tothe demodulator input, an audio amplifier, an automatic volume controlnetwork constructed and arranged to vary the gain of at least one ofsaid cascaded tubes, adjustable means other than said network forvarying the intensity of the Signals transmitted to the demodulator, andmeans between the demodulator output and said audio amplifier foradjusting the intensity of the audio signals transmitted to the audioamplifier.

STUART BALLANTINE.

